Film resistor and method of making

ABSTRACT

Method and apparatus for producing resistors which comprise forming islands of conductive material on a very high ohmic supporting base between a pair of electrodes such that the impedance of the resistor can be adjusted to the desired value and wherein the resistor&#39;&#39;s characteristics do not change due to aging.

United States Patent [191 1111 $8 Krimmel June 18, 1974 [54] FILM RESISTOR AND METHOD OF 3,287,161 11/1966 Schwertz 117/212 MAKING 3,380,156 4/1968 Lood 338/308 3,562,022 2/1971 Shifrin 119/933 Inventor: Eberhard Krlmmel, Pullach, 3,585,088 6/1971 Schwuttke 117/212 Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin OTHER PUBLICATIONS and Munich, Germany Krimmel, Properties of Selfionirradiated Thin Films, 22 Filed: Sept. 1, 1972 141-150;

[21] Appl' 285933 Primary ExaminerE. A. Goldberg Attorney, Agent, or Firm-Hill, Gross, Simpson, Van [30] Foreign Application Priori y ta Santen, Steadman, Chiara & Simpson Sept. 17, 1971 Germany 2146662 [52] [1.8. CI 338/309, 29/620, 117/1 I8, ABSTRACT [51] Im Cl 117/ iigf figg Method and apparatus for producing resistors which [58] Fieid 117/212 comprise forming islands of conductive material on a I very high ohmic supporting base between a pair of 117/93 29/620 333/309 electrodes such that the impedance of the resistor can 56] References Cited be adjusted to the desired value and wherein the resis- UNITED STA S PATENTS tors characteristics do not change due to aging.

2,999,339 9/ 1961 Hensler 338/308 X 10 Claims, 3 Drawing Figures PATENTEDJUNI 81914 3,818,413

pp APPLY F I g. 3 LOW ENE HIGH ENERGY PARTIC PARTICLES SUBSTRATE 1 1 FILM RESISTOR AND METHOD OF MAKING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates in general to apparatus and method for forming resistors and in particular to apparatus and method for forming a very stable resistor of low inductance and capacitance.

2. Description of the Prior Art The use of resistors on substrates has become very desirable as electronic circuits have become smaller and smaller but the resistors of the prior art have suffered from aging effects when produced as layers on substrates and have also had substantial inductance and capacitance. Metal layer resistors are described in the publication Optik, Volume 28 (1968-69), Pages 190 and 191. With prior art metal-layer metal resistors such as described in the publication, the electrical impedance changes with aging. Also, the temperature characteristic and voltage breakdown changes with aging.

SUMMARY OF THE INVENTION The present invention provides an improved method and apparatus for producing electrical resistors on an insulating high ohmic substrate or base in which islands of very small specific conductivity are formed upon a high ohmic supporting base and wherein the resistors thus formed have minimum inductance and capacitance. The resistor is formed between a pair of electrodes attached to the supporting base of high electric resistance and conductive islands are randomly spaced between the electrodes on the supporting base and wherein the surface layer of the supporting base and the islands are subjected to bombarding particles of high energy which remove part of the surface layer of the supporting base. The islands may be produced by deposition of evaporated or sputtered low energy particles which may result from bombardment by high en ergy particles, ions or nuclear particles of a number of materials, or combinations of materials, and wherein the materials as well as the material of the substrate and/or of the supporting base are selected such that charge carrier currents between the electrodes due to an applied electric field pass through the islands and the portions of the supporting base between the islands. The surfaces of the areas of the supporting base between the islands of conductive material are substantially free of individual particles of the island material or of the materials which are utilized during the bombardment.

The resistor of the present invention is produced by deposition of evaporated or sputtered materials or combinations of materials onto the supporting base of high resistivity preferably said bombardment simultaneously occurs with said deposition. In the invention, the fact is utilized that very high resistors can be obtained by applying relatively thin layer islands on a very highly resistant supporting base and wherein the regions of the supporting base between the islands are subjected to radiation damage and wherein the areas between the individual islands are as free as possible of individual deposited particles of material or combinations of materials. Although larger islands may be slightly thicker than smaller islands, all of the islands are relatively thin. Generally the islands will have thicknesses of only one or a few atomic layers in thickness. The dimensions of the islands in the present invention may consist of merely a collection of only a few atoms and an average size island of the layer according to this invention may have a diameter in the order of l nanometer. Also, the distances between the individual islands may be of about the same order. The thickness of the island is critical, particularly, to maintain the voltage independent of the specific conductivity of the layer.

Low energy particles in the invention consist of thermic energy particles which have a maximum of a few electron volts energy. High energy particles are ions or nuclear particles which have previously been accelerated as ions. The energy of these particles is essentially higher than 5 keV and preferably higher than 20 keV. Particles at these energies penetrate into the material of the supporting base into at least several but usually many atomic layers and remain in the material of the supporting base. The location of the particles determines the properties of the insulating layer surface of the supporting base according to this invention and since annealing must be accomplished during a later step in the process of constructing the invention, the heating during annealing must be considered in determining the amount of bombardment.

During construction of the island layer, according to this invention, the rate of absorption of low energy particles by the highly resistant supporting base must be greater than the rate of sputtering of said island layer caused by the bombardment with the high energy particles, otherwise, islands would not be formed during the process. The magnitude of the particle current of the high energy particles determines the thicknesses of the various regions.

If ions are used as the high energy particle, the current density for bombardment will be about 1 milliAmp/cm In case of energy particles which are not charged, a corresponding particle density during bombardment is chosen. Bombardment may occur for several seconds. With such strong bombardment, the radiation damage will be within the range of saturation. Therefore, the island layer formed according to this invention and the final resistor thus formed will be resistant to radiation damage which is particularly advantageous for use of the devices in space travel or under other radiation environment applications.

According to a further development of the invention, the surfaces of the areas between the islands is substantially free of individual adsorbing particles of the material of the islands. This can be obtained by using a highly selected particle density of the current of the high energy particles.

The surfaces of the areas between the islands can also be maintained free from individual absorbing particles by heating the layer (annealing) such that the individual particles will cohese and join to the individual islands by means of diffusing.

Metals or semiconductors are suitable materials for the islands and/or for the bombardment with high energy particles. Electron and hole conducting materials may also be utilized. Favorable results have been obtained when gold, silver, platinum, nickel, iron, chrominum, aluminum and alloys of these with other metals. In addition, carbon, silicon, germanium and compound semiconductors are very suitable. Gold is particularly desirable for this use because of its stability.

The highly resistant supporting base may be formed of very high ohmic silicon and oxides and nitrides of silicon, and in particular, silicon-dioxide is very favorable. In addition, other insulators such as synthetic resins and/or glass can be utilized as material for the highly resistant supporting base.

The apparatus for use in practicing the method of the invention may be the device described in Zeitschrift Fur Angewandte Physik, Vol. 31 (1971), Pages 51 and following.

Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view illustrating the resistor of the invention;

FIG. 2 is a top plan view illustrating the resistor of the invention; and

FIG. 3 is a process step flow chart.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates the resistor of the invention in sectional view. A substrate of high resistant material, as for example silicon, or other materials mentioned above with respect of the base, is designated by numeral 1. A high resistant insulating supporting base or later 3 is formed on the upper surface of the substrate 1 and might be glass, synthetic resin or other insulating material.

In a certain embodiment, the silicon or insulating substrate 1 may also be utilized as the insulating layer and the layer 3 may be dispensed with.

A plurality of islands 5 are formed on the insulating supporting layer 3 or directly on the substrate 1 where such layer 3 is dispensed with and areas between the islands 5 of the insulating layer 3 or of the substrate 1 where such layers are dispensed with are designated by numeral 7. A first electrical conducting electrode 9 is attached to the insulating support layer 3 or directly to the substrate 1 if such layer is dispensed with and a second electrode 11 of electrical conducting material is attached to the layer 3 or substrate 1 if the layer 3 is dispensed with at a position which is remote from the electrode 9 and with the layer 3 and the islands 5 and free areas 7 lying between the electrodes 9 and 11. The electrodes 9 and 11 comprise the input leads to the resistor thus formed.

Upon the application of a voltage between the electrodes 9 and 11, current will flow between the electrodes in the areas 7 between the islands 5 and through the islands 5 where they overlay the layer 3 such that substantially no current flows in the layer 3 beneath the islands 5. This is because the islands 5 are made of metal or semiconductor material such as gold, silver, platinum and have relatively low resistivity. Thus the current will flow in the islands 5 rather than the highly insulating material 3 beneath the islands.

The areas 7 are produced by bombardment with high energy particles which causes the areas 7 to be formed into depressions between the islands 5 due to radiation damage during the bombardment. Also, radiation damage to the upper surface of the layer 3 occurs beneath the islands 5 until the islands 5 are of substantial size so as to protect the areas thereunder so that they are not undercut as much as the free areas 7. The particles and radiation damage are helpful in obtaining good adhesion of the islands 5 to the insulating supporting layer 3 and it is to be realized that FIG. 1 is a schematic view rather than a scale view of the islands 5 and the areas 7 so as to illustrate the principles of the invention. For example, the five islands 5 illustrated in FIG. 1 are greatly enlarged relative to the thickness of the supporting layer 3. Also, the islands 5 are randomly distributed over the surface of the supporting base 3 rather than in straight lines as illustrated in FIG. 1.

FIG. 2 is a plan view of the resistor of the invention wherein the islands 5 and the areas 7 are designated by the numeral 21 which comprises the resistance path between the electrodes 9 and 11.

Because of the high resistance of the layer 21 between the electrodes 9 and I l, resistors of very high impedance can be produced. Such resistors may also be formed in straight lines which produce the smallest amount of inductance and capacitance which is desirable. Due to the construction of the resistors, they are very stable and do not change their characteristics with aging as commonly occurs in prior art devices.

Although minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications that reasonably v and properly come within the scope of my contribution to the art.

I claim as my invention: 1. The method for producing an electrical resistor comprising:

depositing by evaporating or sputtering material onto a portion less than the total surface of a high ohmic supporting base; and applying high energy particles of a material by bombardment into the surface layer of said supporting base such that separated islands of said deposited material will be produced, and wherein ions are used for said bombardment as high-energy particles, and wherein the ion current is large enough to cause the surface of the areas of said insulating supporting base between said islands to be substantially free of particles of the deposited material. 2. The method according to claim 1, wherein the deposition and bombardment are done simultaneously.

3. The method according to claim 1, further including heating said supporting base layer and islands so as to eliminate individual particles of the deposited material from the surface areas between said islands.

4. The method according to claim 1, wherein individual particles of the deposited material is eliminated from the surfaces of the areas between islands by,

means of surface sputtering of the base by said bombardment at an intensity which does not remove said islands.

5. An electrical resistor comprising:

a supporting base of high electric resistivity;

a pair of spaced electrodes formed on said base lying in a first plane;

a conductive layer formed on said supporting base and consisting of a plurality of randomly spaced thin-layer islands of material lying in said first plane between said pair of spaced electrodes; and

base areas of the surface layer of said supporting base between said islands lying in a second plane offset but parallel to said first plane such that upon the application of a voltage between said electrodes current will flow through said islands of said conductivity layer and through said base areas between said islands; and wherein said islands and said areas between said islands occupies substantially less than the total surface of said supporting base. 6. An electrical resistor according to claim 5, wherein the surface of said areas is essentially free from individual particles of the material or materials, or malands have dimensions in the order of one nanometer. 

1. The method for producing an electrical resistor comprising: depositing by evaporating or sputtering material onto a portion less than the total surface of a high ohmic supporting base; and applying high energy particles of a material by bombardment into the surface layer of said supporting base such that separated islands of said deposited material will be produced, and wherein ions are used for said bombardment as high-energy particles, and wherein the ion current is large enough to cause the surface of the areas of said insulating supporting base between said islands to be substantially free of particles of the deposited material.
 2. The method according to claim 1, wherein the deposition and bombardment are done simultaneously.
 3. The method according to claim 1, further including heating said supporting base layer and islands so as to eliminate individual particles of the deposited material from the surface areas between said islands.
 4. The method according to claim 1, wherein individual particles of the deposited material is eliminated from the surfaces of the areas between islands by means of surface sputtering of the base by said bombardment at an intensity which does not remove said islands.
 5. An electrical resistor comprising: a supporting base of high electric resistivity; a pair of spaced electrodes formed on said base lying in a first plane; a conductive layer formed on said supporting base and consisting of a plurality of randomly spaced thin-layer islands of material lying in said first plane between said pair of spaced electrodes; and base areas of the surface layer of said supporting base between said islands lying in a second plane offset but parallel to said first plane such that upon the application of a voltage between said electrodes current will flow through said islands of said conductivity layer and through said base areas between said islands; and wherein said islands and said areas between said islands occupies substantially less than the total surface of said supporting base.
 6. An electrical resistor according to claim 5, wherein the surface of said areas is essentially free from individual particles of the material or materials, or material combinations.
 7. An electrical resistor according to claim 5, wherein said islands are formed of metal.
 8. An electrical resistor according to claim 7, wherein said metal is selected from the group comprising gold, silver and platinum.
 9. An electrical resistor according to claim 5, wherein said islands are formed of semiconductor material.
 10. A resistor according to claim 5, wherein said islands have dimensions in the order of one nanometer. 